Replace item in querystring

Question

I have a URL that also might have a query string part, the query string might be empty or have multiple items.

I want to replace one of the items in the query string

Answer 1

string link = page.Request.Url.ToString();

if(page.Request.Url.Query == "")
    link  += "?pageIndex=" + pageIndex;
else if (page.Request.QueryString["pageIndex"] != "")
{
    var idx = page.Request.QueryString["pageIndex"];
    link = link.Replace("pageIndex=" + idx, "pageIndex=" + pageIndex);
}
else 
    link += "&pageIndex=" + pageIndex;

This seems to work really well.